In the field of laser isotope separation, a vapor of a material such as uranium having a mixture of isotopes is photoinized and the ionized vapor components are then extracted from the vapor through the use of substrates in the form of tails plates and product plates. These components are separated due to the isotopic selectivity of the process. In normal practice, the tails plates are cooled, whereas the product plates run hot due to the temperature of the condensing deposited material and the extractive ion current. The deposited vapor represents both an enriched and depleted isotope composition. In a practical system the deposition of vapor particles onto the substrates is permitted to continue until a significant quantity of material has been deposited before the subsrates are removed from the process to recover the deposited material. Both the enriched and depleted product are recovered in this manner. As the deposition of material progresses during such isotope separation, the mass of the deposition on the substrate increases which, along with other factors occuring in the process, tends to cause the deposition to flake or fall from the substrate unless good adherence is achieved between the deposited layer and the substrate.
It has been typical in the past to operate the tails paltes at a substantially elevated temperature, for example, at or above 450.degree. C. in order to insure an adequate adherence of the deposition to the substrate. With the tails plates at 450.degree. C., the product plates will run substantially higher. In this regard reference is made to commonly assigned U.S. Pat. No. 4,210,814 of John Clifford, entitled "CONTROL OF PYROPHORICITY IN DEPOSITS PRODUCED BY ELECTRON BEAM EVAPORATION OF URANIUM issued July 1, 1980."
The operation of the collecting substrates at such elevated temperatures is undesirable because the elevated temperature increases the warping tendency of the substrates which must be maintained in precise linear alignment in order to insure the proper operation of a laser isotope separation system. More importantly, when operating at high plate-deposition temperatures, large temperature swings occur at the beginning and end of the process cycle and during unavoidable mid-process shutdowns. These large temperatures swings result in the deposit breaking off the collecting substrates. High operating temperatures for all collecting substrates also result in a high temperature radiative surface for the tails plate. Thus in prior systems the tails plate cannot serve as an efficient heat sink for radiative transfer from the product plates. Poor radiative transfer efficiency necessitates the use of high boiling point fluids as active coolants, and the use of additional cooling pipes or exotic heat pipe technology to remove the large amounts of heat which cannot be completely removed by radiative transfer.